= nng_listen(3)
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//
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// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
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// Copyright 2018 Capitar IT Group BV <info@capitar.com>
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//
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// This document is supplied under the terms of the MIT License, a
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// copy of which should be located in the distribution where this
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// file was obtained (LICENSE.txt). A copy of the license may also be
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// found online at https://opensource.org/licenses/MIT.
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//
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== NAME
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nng_listen - create and start listener
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== SYNOPSIS
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[source, c]
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----
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#include <nng/nng.h>
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int nng_listen(nng_socket s, const char *url, nng_listener *lp, int flags);
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----
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== DESCRIPTION
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The `nng_listen()` function creates a newly initialized
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xref:nng_listener.5.adoc[`nng_listener`] object, associated with socket _s_,
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and configured to listen at the address specified by _url_, and starts it.
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If the value of _lp_ is not `NULL`, then
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the newly created listener is stored at the address indicated by _lp_.
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Listeners are used to accept connections initiated by remote dialers.
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An incoming connection generally results in an
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xref:nng_pipe.5.adoc[`nng_pipe`] object being created and attached to the socket _s_.
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Unlike dialers, listeners generally can create many
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pipes, which may be open concurrently.
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The _flags_ argument is ignored, but reserved for future use.
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TIP: While it is convenient to think of listeners as servers, the
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relationship between the listener or dialer is orthogonal to any server or
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client status that might be associated with a given protocol.
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For example, a xref:nng_req.7.adoc[_req_]
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socket might have associated dialers, but might also have associated listeners.
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It may even have some of each at the same time!
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Because the listener is started immediately, it is generally not possible
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to apply extra configuration; if that is needed applications should consider
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using xref:nng_listener_create.3.adoc[`nng_listener_create()`] and
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xref:nng_listener_start.3.adoc[`nng_listener_start()`] instead.
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The created listener will continue to accept new connections, associating
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their pipes with the socket, until either it or the socket _s_ is closed.
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== RETURN VALUES
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This function returns 0 on success, and non-zero otherwise.
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== ERRORS
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[horizontal]
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`NNG_EADDRINUSE`:: The address specified by _url_ is already in use.
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`NNG_EADDRINVAL`:: An invalid _url_ was specified.
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`NNG_ECLOSED`:: The socket _s_ is not open.
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`NNG_EINVAL`:: An invalid set of _flags_ or an invalid _url_ was specified.
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`NNG_ENOMEM`:: Insufficient memory is available.
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== SEE ALSO
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[.text-left]
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xref:nng_dial.3.adoc[nng_dial(3)],
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xref:nng_listener_close.3.adoc[nng_listener_close(3)],
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xref:nng_listener_create.3.adoc[nng_listener_create(3)]
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xref:nng_listener_start.3.adoc[nng_listener_start(3)],
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xref:nng_strerror.3.adoc[nng_strerror(3)],
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xref:nng_listener.5.adoc[nng_listener(5)],
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xref:nng.7.adoc[nng(7)]
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